People have been killing people for all sorts of crazy reasons throughout time.
Again, I agree. But very few have been as effective at it as the Catholic Church or the Muslim jihadists.
Djengis Khan? Nazis? Japaneese medieval warfare? First world war?

In the (to me) very understandable outrage over the way religion can be abused, let us not forget that people kill in great numbers for all other kinds of reasons - greed, powerlust, or to make the world a better place